1. Field of the Invention
This invention pertains to a process for producing hydrocarbons and more particularly to a process for producing hydrocarbons from coal.
2. Prior Art
As a result of the shortage of petroleum products in the world market in recent history it has become more desirable to seek hydrocarbon feedstocks for chemical processes from other sources. One possible source of hydrocarbon feedstock is by the conversion of coal.
A desirable hydrocarbon feedstock is acetylene, C.sub.2 H.sub.2, which is more reactive than ethylene, C.sub.2 H.sub.4, the present primary feedstock for many processes. Acetylene would thus replace ethylene if they were equal in price. Since ethylene is presently made from petroleum, there is great interest in the chemical industry in finding a new source of equivalent chemical feedstock.
Present methods of converting coal to alternative fuels include gasification and devolatilization. Gasification produces primarily carbon monoxide, CO, and hydrogen gas H.sub.2. Gasification processes attempt to minimize the formation of hydrocarbons in the gasification process to avoid fouling the gas flow passages within the equipment. On the other hand, devolatilization of coal not only requires disposal of the large amount of carbon left over after the devolatilization process, but also produces higher hydrocarbons which may be carcinogenic or otherwise hazardous.
All of the processes in the prior art for converting coal to an alternative form have required the addition of heat energy to the coal in order to effect the conversion reaction. One method of adding heat has been through the use of an electric-arc. U.S. Pat. No. 3,384,467 (prior art statement) by Ammann et. al discloses the use of an electric-arc to devolatilize the coal, producing primarily hydrogen gas and unreacted carbon. The disposal of this unreacted carbon and the lack of suitable hydrocarbons present in the reaction product makes this process unsuitable for converting coal to chemical feedstock.
Another method for producing acetylene requires blowing coal with a hydrogen gas carrier through an electric-arc at some 4,900 F. (2704 C.). The reaction products of this reaction are claimed to be 30% acetylene, 20% low to mid BTU gases, such as CO, CH.sub.4, etc. and 50% char, unreacted coal and carbon black. This method, while resulting in a significant fraction of the input constituents being converted to a desirable chemical feedstock, requires a supply of hydrogen gas. The production of hydrogen gas is a costly and complicated process and would be undesirable for use in a large scale facility.
In summary the processes of the prior art either do not convert a significant portion of the coal to the desired hydrocarbon feedstock, or require the addition of hydrogen gas to the coal prior to reaction. The resulting inefficiency and complexity of the prior art processes have made industry reluctant to adopt coal conversion as a means for producing hydrocarbon feedstock.